Synthesis and reactivity of manganese(II) dialkylamido complexes. Crystal and molecular structure of [Mn3(µ-NEt2)6-(µ-Cl)2{Li(thf)2}2]·C7H16(thf = tetrahydrofuran) and [Mn2(µ-NPri2)2(NPri2)2]

Abstract

By reaction of MnCl₂ with LiNR₂(R = Me, Et or Prⁱ) the corresponding dialkylamido complexes were prepared. The compounds [Mn₃(µ-NEt₂)₆(µ-Cl)₂{Li(thf)₂}₂]1(thf = tetrahydrofuran), [Mn₂(µ-NPrⁱ₂)₂-(NPrⁱ₂)₂]2 and [Mn₂(NMe₂)₄(LiCl)]3 were isolated, and the molecular and crystal structures of 1 and 2 determined by single-crystal X-ray diffraction methods. Crystal data: 1, monoclinic, space group C2/c, a= 18.81(1), b= 20.45(2), c= 18.15(2), Å, β= 113.31(8)°, R= 0.063; 2, monoclinic, space group P2/₁c, a= 9.361(2), b= 9.724(2), c= 16.883(2)Å, β= 100.91(1)°, R= 0.046. The pentanuclear compound 1 consists of a trinuclear Mn₃(NEt₂)₆Cl₂ core, built up by edge-sharing of the three co-ordination tetrahedra, which are connected by four bridging diethylamido ligands, and terminally bonded to the Li(thf)₂ moieties via chloride and amido bridges. The homoleptic compound 2 contains two three-co-ordinated manganese atoms, joined by two bridging dialkylamido groups, with an overall planar arrangement of the Mn₂N₄ skeleton. Both 1 and 2 react with CO₂ to give the expected dialkylcarbamato complexes. The reactions of 1–3 with CO result in reductive carbonylation to [Mn(CO)₅]^–. The compounds also catalyse the selective carbonylation of secondary amines to dialkylformamides, a 87% yield of Et₂NC(O)H being obtained from NHEt₂ and CO at atmospheric pressure, in 24 h, in the presence of 1, at room temperature.